T.220.55 notes and example calculation

[david luchini]

How to treat non-range household cooking appliances larger than 12 kW seems not be covered by Table 220.55.

Call me crazy, but I don't think the intent of the Code is that four 12kW ovens would have a demand load of 17kW, but four 12.5kW ovens would have a demand load of 50kW.

Maybe nobody makes household oven appliances greater than 12kW so they didn't worry about it.

 

[tortuga]

Yeah its pretty odd indeed. I never use a general calc in the real world for anything multifamily like that.

 

[tortuga]

There is some interesting history here, prior to 1990
Note 2 was worded as :
"Over 12 KW through 27 KW ranges of unequal ratings"
Then none less than Olaf Ferm had submitted the change proposal for the 1990:

Log # 1961
2- 211 - (Table 220-19, Note 2): Accept
SUBMITTER: Olaf G. Ferm, Ferm's Fast Finder Index
RECOMMENDATION: Change the first two lines to read:
Over 8 3/4 KW through 27 KW ranges of unequal
ratings For ranges individually rated more than 8 3/4
KW and of different ratings, but none . . . (The rest
of the statement to remain as is )
SUBSTANTIATION: In the fourth line of the statement of
Note 2 it says (using 12KW for any range rated less
than 12KW)
This indicates you may have ranges between 8 3/4 KW
and 12 KW in this calculation , but the first two lines
indicate otherwise Note 1 takes ranges over 12 KW
through 27 KW and Note 3 takes ranges over 1 3/4 KW
through 8 3/4 KW
PANEL ACTION: Accept.
VOTE ON PANEL ACTION: Unanimously Affirmative.

So the in the highlighted substantiation refers to Note 3 for ranges under 8.75 KW

Then later in the 1995 ROPA log # 1124
None less than Tom Henry submits a lengthy objection
Saying in part:

did anyone check this calculation before changing
it?

Then goes on with an example:
4 - 8.75 kw ranges
6 - 14 kw ranges
10 - 15 kw ranges

Ultimately it looks like he did not fill out the paperwork correctly and his proposal did not propose to change anything.

PANEL ACTION: Reject.
PANEL STATEMENT: There is no recommendation. The panel
does not agree with the substantiation of the submitter.

So the panel (as usual) did not offer any clarity on weather any size range can be used in that comment.

 

[tortuga]

Tom later in 2004 submits his proposal again:

Report on Proposals – May 2004
2-332 Log #214 NEC-P02
(Table 220-19 Note 2)
Submitter: Tom Henry, Code Electrical Classes, Inc.
Recommendation:
Revise Note 2 as follows:
(Using 12kW for a range(s) rated over 8 3/4 in. to 12kW)

Final Action: Reject
Substantiation:
Note 2 will calculate more correctly if Note 2 stated "(using 12 kW for a range(s) rated over 8 3/4 kW to 12 kW)".
The change was made in 1987 to Note 2 when the SUBMITTER of (2-211) recommended to change the first two lines to read: Over 8 3/4
kW through 27 kW ranges of unequal ratings. For ranges individually rated more than 8 3/4 kW and of different ratings, but none...(The
rest of statement to remain as is).
SUBSTANTIATION: In the fourth line of the statement of Note 2 it says (using 12 kW for any range rated less than 12 kW).
This indicates you may have ranges between 8 3/4 kW and 12 kW in this calculation, that the first two lines indicate otherwise. Note 1
takes ranges over 12 kW through 27 kW and Note 3 takes ranges over 1 3/4 kW through 8 3/4 kW.
PANEL ACTION: Accept.
VOTE ON PANEL ACTION: Unanimously Affirmative.
It is incorrect to state Note 1 takes ranges over 12 kW through 27 kW, Note 1 is solely for ranges "all of the same rating". Note 2 is for
ranges of "unequal ratings".
First, what is the minimum size range? Is there an 8 kW range? Is there a 6 kW range? Is there a 2 kW range? Note 2 presently states "an
average value of rating shall be computed by adding together the ratings of all ranges to obtain the total connected load (using 12 kW
for any range rated less than 12 kW)". In the 1987 Code and all prior Codes, Note 2 stated Over 12 kW through 27 kW ranges of unequal
ratings. It also stated "(using 12 kW for any range rated less than 12 kW)". This allowed ranges of a size smaller than 12 kW, any size
smaller, but you used 12 kW in the calculation as noted. Note 2 always has allowed for ranges between 8 3/4 kW and 12 kW.
The present wording of Note 2 states the range must be over 8 3/4 kW to qualify to use Note 2 in an unequal rating demand calculation.
Example: Calculate the feeder demand for 4 - 8 3/4 kW, 5 - 14 kW and 6 - 15 kW household ranges.
4 x 8.75 kW = 35 kW x 50% Col. B = 17.5 kW
5 - 14 kW = 70 kW
6 - 15 kW = 90 kW
11
160 kW = 160 kW/11 ranges = 14.54 kW or 15 kW average value per range
Note 1 = 11 - 15 kW ranges Col. C = 26 kW
26 kW x 115% = 29.9 kW + 17.5 kW = 47.4 kW demand
By applying the "(using 12 kW for any range rated less than 12 kW)" the demand is only 33 kW compared to a larger demand of 47.4
kW for the same 8 3/4 kW ranges. We followed Note 2 "(using 12 kW for ANY range rated less than 12 kW)".
4 x 12 kW (8.75 kW) = 48 kW
5 - 14 kW
= 70 kW
6 - 15 kW
= 90 kW
15
208 kW = 208 kW/15 ranges = 13.8 or 14 kW average value.
Note 1 = 15 - 14 kW ranges Col. C = 30 kW
30 kW x 110% = 33 kW demand
The actual connected load of this example is 195 kW or 195,000 w/240 V = 812.5 amperes.
To put this in a clearer perspective, a 47.4 kW demand is 47,400 w/240 V = 197.5 amperes. A 33 kW demand is 33,000 w/240 V = 137.5
amperes. Using a 75°C insulation the wire size could be reduced two sizes from #3/0 to #1/0 copper.
197.5 amperes is approximately 24% of the connected load of 812.5 amperes, whereas 137.5 amperes is approximately 17% of the
connected load.
With the present wording of Note "(using 12 kW for any range rated less than 12 kW)" the demand on the feeder would be the same in
the example even if the four 8 3/4 kW ranges were a smaller size of 6 kW. A 6 kW range could qualify to be raised to 12 kW when
applying Note 2 with the present wording of "any range".
If the intent of Note 2 is to be used only when the range is over 8 3/4 kW I feel Note 2 would better meet the intent of the calculation if
the wording was revised removing the words "any range" to read "(using 12 kW for a range(s) rated over 8 3/4 kW to 12 kW)".
Panel Meeting Action: Reject
Panel Statement:
Note 2 only applies to ranges rated over 8 3/4 kW through 27 kW in accordance with the first sentence of the note.
Number Eligible to Vote: 13
Ballot Results: Affirmative: 13

 

[Larry Bohn]

Thanks. I guess that explains note 2 pretty clearly.
Where did you find this information? I may have a few more answers asked by apprentices about specific items in the code.

 

[TAP-ELECTRIC]

Determine the maximum demand for four ranges rated at 8kW, 10kW, 15kW, and 18kW.

Solution

Step 1. Total the range ratings:
12kW (minimum value for 8kW range) + 12kw (minimum value for 10kW range) + 15kW + 18kw = 57kW.

Step 2. Calculate the average rating:
57kW / 4 ranges = 14.25kW

Step 3. Determine the amount of rating above 12kW:
14.25kW - 12kW = 2.25kW

Step 4. Calculate the required demand increase:
5% per kW x 2kW (0.25 kW is not a major fraction) = 10%

Step 5. Calculate the maximum demand:
17kW (Column C demand value for 4 ranges) x 110% = 18.7kW

Where did you get the 110% from plssss

 

[tortuga]

Its from step 4

Determine the maximum demand for four ranges rated at 8kW, 10kW, 15kW, and 18kW.

Solution

Step 1. Total the range ratings:
12kW (minimum value for 8kW range) + 12kw (minimum value for 10kW range) + 15kW + 18kw = 57kW.

Step 2. Calculate the average rating:
57kW / 4 ranges = 14.25kW

Step 3. Determine the amount of rating above 12kW:
14.25kW - 12kW = 2.25kW

Step 4. Calculate the required demand increase:
5% per kW x 2kW (0.25 kW is not a major fraction) = 10%

Step 5. Calculate the maximum demand:
17kW (Column C demand value for 4 ranges) x 110% = 18.7kW

 

[Dennis Alwon]

Where did you get the 110% from plssss

100% + 10% = 110%

You can do it the long way but the answer is the same

100% x 17kw plus 10% x 17kw